1. Technical Field
A present disclosure relates to a single-casing steam turbine and a single-shaft combined-cycle power plant using the single-casing steam turbine that are used in a power generating station or the like.
2. Background Art
As the steam turbine used in the power generating station or the like, a single-casing steam turbine (e.g. single-casing reheat turbine: SRT) is well known, which houses high-pressure blade rows and low-pressure blade rows in a single casing to achieve a shorter axial length and a compact steam turbine.
It is common in a steam turbine to set a clearance based on a fluctuation amount of the distance between a rotary part and a stationary part that is expected under an operation condition so that the rotary part and the stationary part do not contact with each other, and to arrange the rotary part with an offset with respect to the stationary part. This is due to the fact that temperature change of the steam turbine from a stopped state to a rated operation state causes a thermal extension difference between the rotor and the casing, which results in changing of the space between the rotary part and the stationary part.
Therefore, in the case of the single-casing steam turbine, a low-pressure chamber being the heaviest is fixed by an anchor and the overall casing (particularly, the high-pressure chamber and the intermediate-pressure chamber) is allowed to thermally extend freely from the anchor so as to prevent thermal deformation. Meanwhile, the rotor thermally extends from a thrust bearing which rotatably supports the rotor.
Therefore, from a perspective of reducing the thermal extension difference by making the rotor and the casing thermally extend in the same direction, it is necessary to arrange the low-pressure chamber on a side closer to the thrust bearing as the casing thermally extends from the anchor fixed to the low-pressure chamber and the rotor thermally extends from the thrust bearing.
However, by arranging the low-pressure chamber of the single-casing steam turbine on the side closer to the thrust bearing, the high-pressure chamber is inevitably arranged on a side farther from the thrust bearing. For a corresponding amount, the thermal extension difference between the high-pressure chamber and the rotor increases. Thus, it is necessary to provide a large clearance between the rotary part and the stationary part in the high-pressure chamber. However, the large clearance between the rotary part and the stationary part in the high-pressure chamber leads to a decrease in performance of high-pressure blade rows. A blade skeleton of the high-pressure blade rows housed in the high-pressure chamber is particularly small and thus the increased clearance between the rotary part and the stationary part in the high-pressure chamber leads to major decline in the performance of the high-pressure blade rows.
Therefore, for the purpose of reducing the clearance between the rotary part and the stationary part in the high-pressure chamber of the single-casing steam turbine, it is desired to develop a technique for suppressing the thermal extension difference between the high-pressure chamber and the rotor.
In recent years, a combined-cycle power plant with a combination of a steam turbine and a gas turbine is in the spotlight as a power plant used for a thermal power station and the like. The combined-cycle power plant includes a single-shaft power plant in which the steam turbine and the gas turbine are coupled on the same shaft to drive a common generator. In particular, a single-shaft combined-cycle power plant using a single-casing steam turbine has become one of today's mainstream power plants with increasing length of end blades in recent years.
In the single-shaft combined-cycle power plant using the single-casing steam turbine, the thrust bearing is arranged between the steam turbine and the gas turbine and the rotor thermally extends from the thrust bearing. Thus, from a perspective of making the rotor and the casing thermally extend in the same direction, the low-pressure chamber fixed by the anchor from which the casing thermally extends, is arranged on the side closer to the thrust bearing from which the rotor thermally extends, i.e. toward the gas turbine. Therefore, in the single-shaft combined-cycle power plant using the single-casing steam turbine, it is inevitable to secure a large clearance between the rotary part and the stationary part in the high-pressure chamber with respect to the blade skeleton of the high-pressure blade rows in correspondence to the large thermal extension difference between the rotor and the high-pressure chamber arranged on the side farther from the thrust bearing. This generates an issue of the performance decline of the high-pressure blade rows.
Particularly, the combined-cycle power plant is normally arranged in a large-scale thermal power station and the steam turbine is axially large in length. Therefore, in the combined-cycle power plant using the single-casing steam turbine, it is necessary to set the clearance considerably large between the rotary part and the stationary part in the high-pressure chamber and thus the issue of the performance decline of the high-pressure blade rows tends to occur.
In this regard, Patent Literature 1 discloses a space-adjusting unit for adjusting the space between the stationary part and the rotary part of the steam turbine although this is not intended for use in the single-casing steam turbine. In the space-adjusting unit, axial shifting of a flange part projecting from the rotor is detected by an extension difference detector and the casing of the steam turbine is moved by a hydraulic jack based on a detection signal from the extension difference detector.